The present invention relates to a particle surface-modifying method and a particle surface-modifying device which can provide modified particles that have, for example, a superior dispersion property and that are preferably used for ink-jet recording liquid, ball-point pens and marking pens, by modifying (adding hydrophilic groups) the surface of the particles using a modifier such as, for example, an oxidizing agent.
With respect to methods for modifying the surface of various particles, besides those dry-type methods, a method for carrying out polymerization in a liquid phase has been conventionally known, and more specifically, various modifying methods have been put into practice, in which, for example, particles having a hydrophobic property (hydrophobic substance) are treated by a hydrophilic modifier so that a film of the modifier is formed on the surface of the particles so as to impart a hydrophilic property thereto, that is, modifying methods for coating the surface of the particles with a modifier having a hydrophilic property.
With respect to the above-mentioned modifying methods, for example, xe2x80x9cFine Particle Handbookxe2x80x9d (edited by Motoji Jinbo; the first copies of the first edition of which were published by Asakura Shoten K. K. on Sep. 1, 1991), pages 383-394, discloses a surface-modifying method using a kneading and pulverizing method, a spray drying method, etc.
Moreover, for example, xe2x80x9cFine Particle Engineeringxe2x80x94Basics and Application of Dispersionxe2x80x9d (edited by the Japan Powder Industry Technological Association; the first copies of the first edition of which were published by Asakura Shoten K. K. on Jun. 25, 1994), pages 123-136, discloses a method in which: a dissimilar component in powder (surface modifier) is physically bound to the surface of powder particles by using a high-speed rotary impact pulverizer or a dry-type pulverizer, such as a grinding mill, a ball mill, a roll mill, a medium-stirring-type pulverizer, and a jet mill, so that coating-type composite particles the surface of which has been modified in its characteristic are manufactured.
However, in the above-mentioned conventional modifying methods, since, upon treating the particles by using a modifier, the particles are stirred using a stirring device such as stirring blades, the particles are charged through friction, etc. For this reason, the resulting modified particles (hydrophilic particles) tend to adhere to the inner walls of a housing member (hopper) due to its charged state, resulting in a maltransportation; this causes difficulties in handling the particles. Moreover, in the above-mentioned conventional modifying methods, since the modifier is physically bound to the surface of the particles, it takes a very long time to carry out the processes, complex operations are required for carrying out the above-mentioned processes, and expensive devices need to be provided.
In addition, in the above-mentioned conventional modifying methods, the particle size of the resulting modified particles tends to vary depending on the particle size prior to the process, and since particle aggregation, etc. tends to occur upon treating the particles by using a modifier, the resulting modified particles tend to have great particle sizes and become irregular.
Moreover, in the above-mentioned conventional methods, upon carrying out processes in the order of sub-micron, it is difficult to carry out the above-mentioned processes on each of the particles in a stable manner due to the defect that the fine particles are highly susceptible to aggregation.
Furthermore, in the above-mentioned conventional methods, since the surface of the particles is treated using a modifier by stirring the particles and the modifier by using a stirring device, far more amounts of various chemicals, such as a modifier, have to be used beyond what is theoretically required for the surface treatment of the particles, and post processes such as treatment for waste liquid, etc. to a great amount of various residual chemicals. Therefore, another problem of the above-mentioned conventional methods is that the manufacturing costs of the surface-modifying particles (including costs of post treatments) become high.
As described above, any of the above-mentioned conventional modifying methods, that is, the above-mentioned conventional manufacturing method of hydrophilic particles, fails to manufacture uniform hydrophilic particles having a comparatively small particle size at low costs for a short time by using a simple device with simple operations, without causing the particles to be charged.
The present invention has been devised to solve the above-mentioned conventional problems, and its objective is to provide a particle surface-modifying method and a particle surface-modifying method which can manufacture uniform hydrophilic particles having a comparatively small particle size at low costs for a short time by using a simple device with simple operations, without causing the particles to be charged.
In order to achieve the above-mentioned objective, the particle surface-modifying method of the present invention has an arrangement in which, after particles have been suspended in a liquid containing a modifier so as to prepare a suspension, the suspension is heated while being transported so that the surface of the particles is modified by the modifier.
Another particle surface-modifying method of the present invention has an arrangement in which, after particles have been suspended in a liquid containing a modifier so as to prepare a suspension, the liquid is evaporated while the suspension is being transported so that the surface of the particles is modified by the modifier.
In the above-mentioned method, by heating the suspension while being transported, the liquid in the suspension can be, for example, partially nuclear boiled during the transporting process with the particles serving as nuclei, or evaporated, successively in a stable manner, while the suspension is being transported. Thus, in this method, the surface of the particles is heated in the presence of the modifier at the portions being nuclear boiled or evaporated so that it becomes possible to efficiently modify the surface of the particles by using the modifier, and consequently to obtain surface-modified particles.
Moreover, in the above-mentioned method, the respective particles tend to aggregate with each other when they have a small particle size (in particular, in not more than the sub-micron order); however, while the respective aggregating particles are being dispersed by applying an external force exerted by an abrupt volume expansion due to nuclear boiling by application of heat, for example, by a volume expansion of 1000 times exerted by evaporated water, the surface of each of the particles is modified by the modifier. For this reason, the above-mentioned method makes it possible to eliminate the conventional stirring process for restricting the aggregation, and consequently, to avoid charging of the particles.
As a result, the above-mentioned method makes it possible to manufacture uniform surface modified particles having a comparatively small particle size at low costs for a short time by using simple operations, while preventing the particles from being charged.
In order to achieve the above-mentioned objective, the particle surface-modifying device of the present invention is provided with a particle suspension section for preparing a suspension in which particles are suspended in a liquid containing a modifier and a modifying section for preparing surface modified particles by modifying the surface of the particles by using the modifier, wherein the modifying section modifies the surface of the particles by using the modifier while allowing the suspension from the particle suspension section to boil, and transports the surface modified particles by using a pneumatic transport derived from evaporated gas from the liquid in the suspension.
With the above-mentioned arrangement, the surface modified particles are prepared by modifying the surface of the particles by using the modifier while the suspension, prepared by the particle suspension section, is being allowed to boil; therefore, in the same manner as the above-mentioned method of the present invention, it becomes possible to prepare uniform surface modifying particles having a comparatively small particle size in a more stable manner.
In addition, in the above-mentioned arrangement, the surface modified particles are transported by using the pneumatic transport derived from evaporated gas from the liquid in the suspension; therefore, the transportation of the surface modified particles is simplified, and the modifying section can be provided, for example, as a tube form extending in a perpendicular direction, with a result that the floor space of the modifying section can be reduced.
Consequently, in the above-mentioned arrangement, the application of the pneumatic transport derived from the evaporated gas makes it possible to simplify the device construction and also to miniaturize the device and reduce the occupied space.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.